Atlantic salmon (Salmo salar) COSEWIC assessment and status report: chapter 8

Distribution

Global Rangeiv

Atlantic Salmon originally occurred in every country whose rivers flow into the North Atlantic Ocean and Baltic Sea (Mills 1989) (Figure 10). The range of Atlantic Salmon extended southward from northern Norway and Russia along the Atlantic coastal drainage to Northern Portugal including rivers in both France and Spain (MacCrimmon and Gots 1979). In North America, the range of the anadromous Atlantic Salmon was northward from the Hudson River drainage in New York State, to outer Ungava Bay in Quebec (MacCrimmon and Gots 1979). Non-migratory or non-anadromous forms of Atlantic Salmon occur in areas of Europe, and North America.

The current distribution is reduced compared to the historical range and the number of rivers supporting spawning runs in each country, as well as the estimated population sizes, are much lower than those recorded historically.

Figure 10: Current Global Distribution of Atlantic Salmon (Salmo salar), Excluding Canada

Map showing current global distribution of Atlantic Salmon, excluding Canada. Arrows indicate migration patterns of wild salmon.

Arrows indicate migration patterns of wild salmon. The total number of historical salmon-bearing rivers worldwide is indicated at the right of map. COSEWIC (2006).

Canadian Rangev

The Canadian range is roughly one-third the area of the total global range, and extends northward from the St. Croix River (at the border with Maine, U.S.A.) to outer Ungava Bay of Quebec, plus one population in Eastern Hudson Bay (MacCrimmon and Gots 1979, Scott and Crossman 1973). Salmon occupy or have occupied at least 700 rivers in the Canadian rangevi, not including many smaller rivers that have been occupied intermittently.

Extent of Occurrence and Area of Occupancy

With the exception of the extinct Lake Ontario population (DU 11) the extent of occurrence of each of the Atlantic Salmon DUs includes a large portion of the North Atlantic Ocean, substantially greater than 20,000 km2. Accurate estimates of area of occupancy during the most spatially confined life history stages, spawning and early rearing of juveniles, are not possible for the great majority of rivers occupied by salmon, based on current knowledge. To determine whether index of area of occupancy (IAO) might fall below important thresholds (2,000 km2 or 500 km2) for status assessments of individual DUs, estimates of IAO were made for eight DUs with small numbers of rivers. DU 15 (Inner Bay of Fundy), for which area of occupancy was previously estimated to be 9 km2 (COSEWIC 2006b) was not included in this analysis. IAO was estimated using 2 x 2 km grids overlaying potential river habitat, beginning with main stems of known spawning rivers. If these summed to less than 2,000 km2 for any DU, tributaries were also included in the analysis. Where available, information about barriers limiting access of migratory salmon was taken into account.

Using this approach, estimated IAO exceeded the 2,000 km2 threshold for each of the following six DUs (see Technical Summaries for exact values of estimates): DU 1, 7, 8, 9, 14, 16. Two DUs 10 (Inner St. Lawrence) and13 (Eastern Cape Breton), had estimated IAOs below 2,000 km2, 1,552 and 1,684 km2, respectively.




Footnotes

iv This section was taken from COSEWIC (2006a).
v This section was taken from COSEWIC (2006b).
vi Note that the number of salmon rivers presented by the WWF does not correspond with the estimate provided by COSEWIC (2006b) in Figure 2

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